Telephone line interface circuits typically include a hook switch circuit for conducting relatively large levels of current between the tip and ring terminals of the telephone line in order to generate an off-hook state. For example, when a computer initiates a telephone call, it drives the hook switch circuit, via interface circuitry, in order to activate the telephone line. These hook switch circuits exist on the line side of the telephone line interface circuitry, but are typically driven from the modem side of the interface circuitry. The modem and line sides of the telephone line interface circuitry are electrically isolated from one another and the hook switch circuit must be driven across the isolation barrier. The hook switch circuits are typically either current driven devices, e.g. an optoisolator, relay/transformer, or capacitive driven devices, where the isolation barrier is capacitive. Other types of circuits also involve electrical isolation barriers.